The present invention relates to a finisher for use with a copier, printer or similar image forming apparatus and operable to staple or otherwise finish paper sheets which are sequentially driven out of the apparatus.
A finisher of the kind described is generally constructed such that paper sheets sequentially fed out of an image forming apparatus are stacked on a staple tray and then stapled, and the stapled paper stack is let fall onto a discharge tray disposed below the staple tray. This type of finisher is disclosed in Japanese Patent Laid-Open Publication (Kokai) Nos. 62-20046, 62-191375, 62-176246, 62-290669, 59-82263, and 63-101268 by way of example.
The prior art finisher described above has some problems left unsolved, as follows.
(1) The staple tray overlying the discharge tray interferes with the operator's access to the finished paper stack on the discharge tray. The operator cannot reach the finished paper stack without bending down, resulting in troublesome work.
(2) A stapler staples a paper stack at a predetermined position without exception. Especially, there is a fear that the actual stapling position differs from an expected position, depending on the image forming direction or writing direction on the paper sheets.
(3) A problem with a prior art finisher of the type discharging a stapled paper stack onto an overlying tray is that an extra paper transport path and, therefore, an extra space is needed because the tray is disposed above the stapled paper stack.
(4) When the stapled paper stack is directly discharged from the stapler in order to eliminate the extra paper discharge path, it is likely that the paper sheets are creased and/or the number of paper sheets of a stack which can be discharged is decreased.
(5) It is impossible to detect a stapling error and a jam of a stapled stack accurately and efficiently.
(6) A finisher of the type disclosed in Japanese Patent Laid-Open Publication Nos. 82263/1984, 290669/1987 and 101268/1988 binds a stack of sheets only at a predetermined position by a single stapler which is fixed at one corder of the finisher. While this type of finisher is inherently simple in construction, it cannot bind a sheet stack at a position other than the predetermined position. In light of this, there has been proposed a finisher having two staplers, as taught in, for example, Japanese Patent Laid-Open Publication Nos. 13364/1989 and 185774/1988. Although the dual stapler type finisher enhances productivity by binding a sheet stack at two positions at the same time, it is expensive due to the two staplers.